The present invention relates to a golf club shaft and a set of golf clubs.
Conventionally, in order to adjust a swing balance of a golf club shaft, a weight made of metal is attached to an end portion or a grip portion of the golf club shaft so as to adjust the weight balance.
However, when the above conventional method is adopted in which only the weight is adjusted, it is impossible to adjust a bend balance of the shaft. Recently, golf club shafts made of carbon fiber are used. Therefore, the bounce property of the golf club shaft is high. On the other hand, the shaft made of carbon fiber lacks tenacity, and further it is impossible to accumulate power in the shaft in the process of swinging the golf club. For the above reasons, it is difficult for a golfer to hit a ball at good timing, and the golfer can not swing the golf club stably. Since the golfer can not swing the golf club stably, it is difficult for him to get distance and further the direction of a golf ball, which has been hit by the golfer, tends to fluctuate greatly.
When a weight member made of metal is only attached to a golf club shaft like a conventional golf club shaft, the weight member is damaged and detached from the golf club shaft by the bend repeatedly given to the shaft.
The present invention has been accomplished to solve the above problems. It is an object of the present invention to provide a golf club shaft characterized in that: tenacity can be exhibited by the golf club shaft; power can be accumulated in the process of swinging the golf club; it is easy for a golfer to hit a ball with the golf club; it is possible for the golfer to get distance when he hits a ball; the direction of a ball, which has been hit with the golf club, can be stabilized; the layer member is not separated from the golf club shaft; and damage of the layer member is prevented, so that the mechanical strength and durability of the golf club can be enhanced.
It is another object of the present invention to provide a set of golf clubs characterized in that the adjustment of swing balance can be effectively conducted among the golf clubs.
In order to solve the above problems, the present invention is to provide a golf club shaft comprising: a main body layer on which a first fiber-reinforced prepreg sheet, the reinforcement fiber of which is impregnated with synthetic resin, is rolled; and an adjustment layer on which a second fiber-reinforced prepreg sheet, the reinforcement fiber of which is impregnated with synthetic resin, is rolled, the adjustment layer being arranged inside the main body layer or in an intermediate portion of the main body layer, wherein the specific gravity of the second fiber-reinforced prepreg sheet is higher than that of the first fiber-reinforced prepreg sheet, the elasticity of the second fiber-reinforced prepreg sheet is lower than that of the first fiber-reinforced prepreg sheet, and a ratio of the volume of the adjustment layer to the volume of all layers is in a range from 10 to 90%.
Also, the present invention is to provide a golf club shaft comprising: a main body layer on which a first fiber-reinforced prepreg sheet, the reinforcement fiber of which is impregnated with synthetic resin, is rolled; and an adjustment layer on which a second fiber-reinforced prepreg sheet, the reinforcement fiber of which is impregnated with synthetic resin, is rolled, the adjustment layer being arranged inside the main body layer or in an intermediate portion of the main body layer, wherein the main body layer includes an axial direction fiber layer on which a fiber-reinforced prepreg sheet, the axial direction reinforcement fiber of which is impregnated with synthetic resin, is rolled, and the specific gravity of the second fiber-reinforced prepreg sheet is higher than that of the fiber-reinforced prepreg composing the axial direction fiber layer, the elasticity of the second fiber-reinforced prepreg sheet is lower than that of the fiber-reinforced prepreg composing the axial direction fiber layer, and the thickness of the adjustment layer is not lower than 25% of the thickness of the axial direction fiber layer of the main body layer.
Also, the present invention is to provide a set of golf clubs, each golf club comprising: a main body layer on which a first fiber-reinforced prepreg sheet, the reinforcement fiber of which is impregnated with synthetic resin, is rolled; and an adjustment layer on which a second fiber-reinforced prepreg sheet, the reinforcement fiber of which is impregnated with synthetic resin, is rolled, the adjustment layer being arranged inside the main body layer or in an intermediate portion of the main body layer, wherein a ratio of volume of the adjustment layer is increased as the golf club number is increased.
Also, the present invention is to provide a set of golf clubs, each golf club comprising: a main body layer on which a fiber-reinforced prepreg sheet, the reinforcement fiber of which is impregnated with synthetic resin, is rolled, wherein the flexural rigidity of the shaft from an end portion to a position distant from the end portion by 20 cm is reduced as the golf club number is increased.
The characteristic of the golf club shaft and the set of golf clubs of the present invention is an adjustment layer arranged inside or in the intermediate portion of the main body layer on which a fiber-reinforced prepreg sheet is rolled, wherein the specific gravity (density) of the fiber-reinforced prepreg sheet of the adjustment layer is higher than that of the fiber-reinforced prepreg sheet of the main body layer, and the elasticity of the fiber-reinforced prepreg sheet of the adjustment layer is lower than that of the fiber-reinforced prepreg sheet of the main body layer. In this case, the intermediate portion of the main body layer is defined as an intermediate layer arranged between a plurality of layers composing the main body layer. In this connection, it is possible to control the specific gravity and elasticity of the fiber-reinforced prepreg sheet by appropriately adjusting types of the reinforcement fiber and resin impregnated into the reinforcement fiber and also by appropriately adjusting a quantity of resin impregnated into the reinforcement fiber.
In the golf club shaft of the first embodiment of the present invention, a ratio of the volume of the adjustment layer to the volume of all layers is in a range from 10 to 90%. It is preferable that the ratio of the volume of the adjustment layer to the volume of all layers is in a range from 20 to 80%. In the case where the adjustment layer is formed over the entire length of the shaft, a ratio of the cross-sectional area of the adjustment layer to the cross-sectional area of the shaft in the radial direction may be used instead of the volume of the adjustment layer. When it is difficult to judge by the area of the cross-section in the radial direction, it is possible to find the ratio by the volume of the reinforcement fiber or the area of the cross section in the axial direction.
When the volume (cross-sectional area) of the adjustment layer is smaller than 10%, it is impossible to obtain a feeling of weight by which a low handicapper can be satisfied. Further, when the volume of the adjustment layer is smaller than 10%, it is impossible to provide a sufficiently high effect of shock reduction. When the volume of the adjustment layer exceeds 90%, it is possible to provide an effect of shock reduction, however, the golf club becomes too heavy, and the golf club is not suitable for a golfer to use over a long period of time. Accordingly, the volume of the adjustment layer exceeding 90% is not preferable.
According to the first embodiment of the present invention, it is possible to provide a golf club shaft characterized in that: the balance of swing is good; tenacity is sufficiently high; and power can be accumulated when a golfer swings the golf club. According to the first embodiment of the present invention, it is possible to provide a golf club in which the layers are not separated from each other and the permanent set in fatigue of the shaft can be prevented.
In the golf club shaft of the second embodiment of the present invention, the thickness of the adjustment layer is not lower than 25% of the thickness of the axial direction fiber layer of the main body layer. It is preferable that the thickness of the adjustment layer is in a range from 30 to 80% of the thickness of the axial direction fiber layer of the main body layer. When the thickness of the adjustment layer is smaller than 25%, the golf club shaft becomes too light. Therefore, it is impossible to provide an appropriate feeling of weight, and further it is impossible to provide a good tenacity and bend.
According to the second embodiment of the present invention, it is possible to provide a golf club shaft characterized in that: the bend and weight balance is good when a golfer swings the golf club; tenacity is sufficiently high; and power can be accumulated when a golfer swings the golf club. According to the second embodiment of the present invention, it is possible to provide a golf club in which the layers are not separated from each other and the mechanical strength of the golf club can be enhanced.
In the golf club shaft of the third embodiment of the present invention, a ratio of volume of the adjustment layer is increased as the golf club number is increased.
According to the third embodiment of the present invention, it is possible to provide the same effect as that of the first and the second embodiment, and further the directivity of a ball, which has been hit by a golfer with a short iron golf club, can be stabilized. Furthermore, when a ball is hit by a golfer with a long iron golf club, it is possible to get distance and the directivity can be stabilized.
It is preferable that the total weight of the golf club shaft of the present invention is 70 to 140 g, and it is more preferable that the total weight of the golf club shaft of the present invention is 80 to 140 g.
When the golf club shaft and the set of golf clubs of the present invention are used, although the golf club shaft is composed of layers of prepreg, the bend and weight balance is so good that tenacity can be provided and power can be accumulated in the process of swinging the golf club.